Polyphenylene ethers are generally obtained by oxidative polymerization of phenols in an aromatic hydrocarbon solvent or a mixed solvent of an aromatic hydrocarbon and an alcohol in the presence of a complex catalyst containing copper, manganese, or cobalt and in the copresence of an oxygen-containing gas.
The reaction mixture of the aforesaid polymerization inevitably contains impurities which impair characteristics of polyphenylene ethers in no small quantities, such as a residue of the catalyst used and diphenoquinones as by-products. These impurities have been generally removed by contacting the polymerization reaction mixture with a catalyst decomposing agent or a reducing agent, such as mineral acids, e.g., hydrochloric acid, sulfuric acid, etc., or organic acids, e.g., acetic acid.
It has also been proposed to remove a metallic component of the catalyst by using a chelating agent as disclosed in German Patent Nos. 2,460,323 and 2,532,477, U.S. Pat. Nos. 4,026,870 and 4,071,500, and European Patent Nos. 81,140 and 103,275.
However, the treatment with acids or chelating agents involves use of alcohols in a large quantity relative to the polymerization mixture, which leads to an increased cost for alcohol recovery and ultimately to bad economy. Further, since the polyphenylene ethers precipitate upon addition of alcohols in the form of considerably fine particles, special additional equipments are required for drying and transportation of such fine particles in order to cope with problems such as dusting. Furthermore, such fine particles cause many troubles in molding, such as starved feeding from a hopper, insufficient feeding to a granulator, and the like. If the amount of the alcohol to be used is reduced, the polyphenylene ether is agglomerated in subsequent steps, e.g., a drying step, and becomes difficult to handle.